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EP0765970A2 - Dispositif de commande hydraulique pour engin de chantier - Google Patents

Dispositif de commande hydraulique pour engin de chantier Download PDF

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Publication number
EP0765970A2
EP0765970A2 EP96203352A EP96203352A EP0765970A2 EP 0765970 A2 EP0765970 A2 EP 0765970A2 EP 96203352 A EP96203352 A EP 96203352A EP 96203352 A EP96203352 A EP 96203352A EP 0765970 A2 EP0765970 A2 EP 0765970A2
Authority
EP
European Patent Office
Prior art keywords
rotational speed
hydraulic
target
displacement
control
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP96203352A
Other languages
German (de)
English (en)
Other versions
EP0765970A3 (fr
EP0765970B1 (fr
Inventor
Akira Tatsumi
Seiji Tamura
Mitsuo Kihara
Kazuhiro Ichimura
Shigetaka Nakamura
Hiroshi Onoue
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hitachi Construction Machinery Co Ltd
Original Assignee
Hitachi Construction Machinery Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hitachi Construction Machinery Co Ltd filed Critical Hitachi Construction Machinery Co Ltd
Publication of EP0765970A2 publication Critical patent/EP0765970A2/fr
Publication of EP0765970A3 publication Critical patent/EP0765970A3/fr
Application granted granted Critical
Publication of EP0765970B1 publication Critical patent/EP0765970B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2221—Control of flow rate; Load sensing arrangements
    • E02F9/2225—Control of flow rate; Load sensing arrangements using pressure-compensating valves
    • E02F9/2228—Control of flow rate; Load sensing arrangements using pressure-compensating valves including an electronic controller
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2221—Control of flow rate; Load sensing arrangements
    • E02F9/2232—Control of flow rate; Load sensing arrangements using one or more variable displacement pumps
    • E02F9/2235—Control of flow rate; Load sensing arrangements using one or more variable displacement pumps including an electronic controller
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2221—Control of flow rate; Load sensing arrangements
    • E02F9/2239—Control of flow rate; Load sensing arrangements using two or more pumps with cross-assistance
    • E02F9/2242—Control of flow rate; Load sensing arrangements using two or more pumps with cross-assistance including an electronic controller
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2246—Control of prime movers, e.g. depending on the hydraulic load of work tools
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2278—Hydraulic circuits
    • E02F9/2285—Pilot-operated systems
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2278—Hydraulic circuits
    • E02F9/2292—Systems with two or more pumps
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2278—Hydraulic circuits
    • E02F9/2296—Systems with a variable displacement pump
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H61/00—Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing
    • F16H61/38—Control of exclusively fluid gearing
    • F16H61/40—Control of exclusively fluid gearing hydrostatic
    • F16H61/46—Automatic regulation in accordance with output requirements
    • F16H61/472—Automatic regulation in accordance with output requirements for achieving a target output torque
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B3/00—Engines characterised by air compression and subsequent fuel addition
    • F02B3/06—Engines characterised by air compression and subsequent fuel addition with compression ignition

Definitions

  • This invention relates to a hydraulic control apparatus for a hydraulic construction machine for which a load sensing control and an input torque limiting control can be performed.
  • a wheel type hydraulic shovel for example, as shown in Fig. 10 has been known as a hydraulic construction machine equipped with the above type of hydraulic control apparatus.
  • a reforence numeral 4 represents a hydraulic motor for vehicle travelling, and rear wheels 103 are driven through a transmission 101 and a propeller shaft 102 by the rotation of the hydraulic motor 4 to allow a vehicle to travel.
  • a boom 104 serving as a part of a front attachment is upwardly and downwardly moved through a lengthening and shortening operation of a boom cylinder 21.
  • work a digging work and the like using the front attachment while the vehicle does not travel
  • these works are distinguished from a term "travel”.
  • Fig. 11 shows a hydraulic circuit for the travel and the work of the hydraulic shovel as described above, and a reference numeral 1 represents a variable displacement hydraulic pump which is driven by a diesel engine 27.
  • the rotational speed of the engine 27 is controlled through rotational member of a governor lever 27b of a governor 27a which is driven, in accordance with an manipulation amount of a fuel lever (not shown) or an operation amount of an acceleration pedal 6a for the travel (hereinafter referred to as a travelling pedal), by a pulse motor 28.
  • a variable displacement hydraulic pump 1 discharges an oil whose flow amount corresponds to the engine rotational speed and the displacement thereof.
  • the discharged oil is communicated through a travel-control valve 2 to the hydraulic motor 4, and further communicated through a work-control valve 20 to a boom-driving hydraulic cylinder 21.
  • the load sensing control is characterized in that the displacement (hereinafter also referred to as "tilt angle") of the variable displacement hydraulic pump 1 is so controlled that the difference pressure between front and rear stages of the travel-control valve 2 or the work-control valve 20, that is, the difference pressure between a pressure (pump pressure) at an inlet port of the control valve 2, 20 and a pressure (load sensing pressure) at an outlet port thereof is fixed to a constant value to thereby keeping the pump pressure to a value higher than the load sensing pressure by a predetermined target value.
  • the load sensing pressure is a pressure selected by a shuttle valve 29 and higher one of load pressures of the hydraulic motor 4 and the hydraulic cylinder 21.
  • the system for carrying out the load sensing control as shown in Fig. 11 is equipped with a load sensing regulator 11 whose switching operation is carried out in accordance with the difference pressure between the pump pressure and the load sensing pressure.
  • the load sensing regulator 11 When the difference pressure between the pump pressure and the load sensing pressure exceeds a pressure which is set by a spring 11a, the load sensing regulator 11 is switched to a position b in accordance with the pressure.
  • the pump pressure is communicated to a servo cylinder 12, and the displacement of the hydraulic pump 1 is reduced through a lengthening operation of the servo cylinder 12, so that the delivery flow rate of the pump is reduced.
  • the load sensing regulator 11 is switched to a position a, and the servo cylinder 12 is intercommunicated to a tank. Consequently, the displacement as described above is increased, and thus the pump delivery flow rate is also increased.
  • the tilt angle of the pump is so controlled that the pump delivery flow rate is equal to a required flow rate of the control valve 2 or 20, so that a surplus flow rate of oil can be prevented from being delivered and vain use of the oil due to diaphragm loss can be prevented to improve fuel consumption and operational performance.
  • a delivery oil from the hydraulic pump 5 is communicated to a pilot port 2a of a pilot-type control valve 2, so that the control valve 2 carries out its switching operation by a stroke amount corresponding to a pilot oil pressure.
  • the delivery oil from the variable displacement hydraulic pump 1 is supplied through a conduit 91, a pressure compensating valve 23, the control valve 2, a conduit 92 and a counterbalance valve 3 to the hydraulic motor 4 to allow the vehicle to run.
  • the engine rotational speed is controlled in accordance with the operation amount by which the travelling pedal 6a is depressed, so that the travelling speed of the vehicle is dependent on the operation amount of the travelling pedal 6a.
  • the delivery oil from the hydraulic pump 1 is communicated through the conduit 91, the pressure compensating valve 24, a conduit 94 and the control valve 20 to the boom-driving hydraulic cylinder 21, and the boom 104 as shown in Fig. 10 is upwardly and downwardly moved through the lengthening and shortening operation of the hydraulic cylinder 21.
  • the pressure compensating valves 23 and 24 enable the hydraulic pump 1 to supply the hydraulic motor 4 and the hydraulic cylinder 21 with pressures higher than the load pressures thereof by a predetermined pressure, respectively, so that both actuators can be operated independently of each other.
  • the hydraulic control apparatus as shown in Fig. 11 is equipped with a torque control servo valve 25 for carrying out the input torque limiting control, and the servo valve 25 is supplied with the delivery pressure of the hydraulic pump 1 as a pilot pressure.
  • the pilot pressure acting on the servo valve 25 exceeds a pressure set by a limit torque setting spring 25a, the servo valve 25 is switched from the c-position to the d-position as shown in the figure.
  • the delivery pressure of the hydraulic pump 1 acts on the servo cylinder 12, whereby the displacement of the hydraulic pump 1 is reduced, and the torque of the hydraulic pump 1 is kept in a range of the output torque of the engine 27, thereby preventing an overload from being applied to the engine 27.
  • This operation is referred to as the input torque limiting control.
  • the displacement of the hydraulic pump is so controlled that it is equal to smaller one of the target displacement by the load sensing control (first target displacement) and the target displacement by the input torque limiting control (second target displacement), and through this operation the improvement in fuel consumption and operating performance and the prevention of overload acting on the engine 27 are accomplished.
  • a reference numeral 26 represents an unload valve which is driven by the difference pressure between the pump pressure and the load sensing pressure
  • reference numerals 31a and 31b represent a cross-over load relief valve
  • CJ represents a center joint.
  • the hydraulic control apparatus equipped with the load sensing control and the input torque limiting control systems is so constructed that the maximum value of the displacement of the variable displacement hydraulic pump 1 is limited by a value which is determined by the servo valve 25 at the input torque limiting control system side, and in a range below this maximum value the displacement of the variable displacement hydraulic pump 1 is set to the displacement which is determined by the load sensing regulator 11 at the load sensing control system side.
  • the displacement of the variable hydraulic pump 1 is so controlled as to be uniformly set to any one of the input torque limiting control value and the load sensing control value on the basis of the operation amount of the travelling pedal, the operation amount of the manipulating lever or the circuit pressure condition irrespective of variation of an operating circumstance such as "travel" or "work", or an operator's preference.
  • the displacement of the hydraulic pump 1 is automatically decreased so as to prevent the rise-up of the difference pressure as described above even when the rotational speed of the engine 27 is heightened and thus the pump delivery flow rate is increased while it is increased so as to prevent the drop of the difference pressure even when the rotational speed of the engine 27 is lowered and thus the pump delivery flow rate is decreased.
  • the pump delivery flow rate remains constant even when the engine rotational speed is varied, and the driving speed of the front attachment (for example, boom) is not varied, whereby an efficiency during the work is low.
  • the speed of the front actuator can be controlled through the control of the engine rotational speed in a state where a difference pressure which is beforehand set does not occur even when the tilt angle of the hydraulic pump 1 is increased to the maximum value, or in a case where a target flow rate exceeds a torque limiting flow rate (in a saturation state).
  • An object of this invention is to provide a hydraulic control apparatus for a hydraulic construction machine in which, when a special operating condition is detected, a load sensing control is inhibited and a displacement of the hydraulic pump is controlled through an input torque limiting control.
  • Fig. 1 is a block diagram showing a pump control system for a hydraulic control apparatus according to a first embodiment of this invention.
  • Fig. 2 is a diagram showing the whole construction of the hydraulic control apparatus.
  • Fig. 3 is an enlarged view of a part of Fig. 2.
  • Fig. 4 is a block diagram showing a pump control system for a hydraulic control apparatus according to a second embodiment of this invention.
  • Fig. 5 is a block diagram showing a pump control system for a hydraulic control apparatus according to a third embodiment of this invention.
  • Fig. 6 is a block diagram showing an engine control system.
  • Fig. 7 is a flowchart for a control procedure for an engine rotational speed.
  • Fig. 8 is a detailed block diagram showing an input torque control portion in the first to third embodiments.
  • Fig. 9 is a detailed block diagram showing the input torque control portion to solve a problem occurring in the input torque control portion.
  • Fig. 10 is a side view of a wheel-type hydraulic shovel.
  • Fig. 11 is a diagram showing a conventional hydraulic control apparatus.
  • Fig. 12 is a block diagram showing a pump control system for a hydraulic control apparatus according to a variation of the third embodiment of this invention.
  • the hydraulic control apparatus is constructed such that the displacement is usually controlled to be set to smaller one of a first target displacement calculated in a load sensing control system and a second target displacement calculated in an input torque limiting control system, and when higher responsibility is required a limitation is imposed on the first target displacement to increase a stand-by flow rate, and then the displacement is controlled to be set to smaller one of a limit value larger than the first target displacement and the second target displacement.
  • Fig. 2 is a diagram showing the whole construction of a hydraulic control apparatus for a wheel-type hydraulic shovel to which this invention is applied
  • Fig. 3 is an enlarged diagram of a part of the control apparatus.
  • the same elements as those of Fig. 11 are represented by the same reference numerals, and the difference therebetween will be mainly described.
  • a tilt angle of a variable displacement hydraulic pump 1, that is, the displacement thereof is controlled by a tilt angle control device 40.
  • the tilt angle control device 40 comprises a hydraulic pump 41 which is driven by an engine 27, a pair of electromagnetic valves 42 and 43, and a servo cylinder 44 whose piston position is controlled by a pressured oil from the hydraulic pump 41 in accordance with a switching operation of the electromagnetic valves 42 and 43.
  • the tilt angle of the hydraulic pump 1 is controlled in accordance with the piston position of the servo cylinder 44.
  • the switching operation of the pair of the electromagnetic valves 42 and 43 is controlled by a controller 50 mainly comprising a microcomputer.
  • a forward/reverse travel switching valve 8A comprises an electromagnetic type of valve, and it is switched from an N-position to an F-position or R-position when a forward/reverse travel switching switch SW1 at a driver sheet is switched from an N-position to an F-position or R-position.
  • a control valve 20A for a work comprises a pilot-type valve, and a switching direction and a stroke amount are controlled by pilot pressure output from a pressure reducing valve in accordance with the operation amount of a manipulation lever 58.
  • SW2 represents a brake switch, and it is switched on by operator's manipulation at the work while it is switched off at a vehicle travelling.
  • SW3 represents a response speed selecting switch, and it is switched on when a quick mode is set to increase the stand-by flow rate as described later while it is switched off when a normal mode is set to seriously consider fuel consumption and noise.
  • the output signals of these switches SW2 and SW3 are commonly input to the controller 50.
  • an operating condition of the vehicle such as the work or the travel is electrically detected, and the displacement of the hydraulic pump is electrically controlled.
  • the displacement of the hydraulic pump is controlled by inputting the signals of the switches as described above and a group of sensors as described later to the controller 50 and executing various calculations in the controller 50 to drive various kinds of actuators.
  • a reference numeral 51 represents a tilt angle sensor for detecting a tilt angle ⁇ s of the hydraulic pump 1
  • a reference numeral 52 represents a pressure sensor for detecting a delivery pressure Pp of the hydraulic pump 1
  • a reference numeral 53 represents a rotational speed sensor for detecting a rotational speed Nr of the engine 27, and a reference numeral 54 represents a difference-pressure sensor for detecting a difference pressure ⁇ PLS between the delivery pressure of the hydraulic pump 1 and the maximum load pressure of the actuator (which is larger one of a load pressure of the hydraulic motor 4 and a load pressure of the hydraulic cylinder 21 and selected by the shuttle valve 29).
  • a reference numeral 55 represents a potentiometer for detecting a control rotational speed N ⁇ on the basis of a displacement amount of the governor lever 27b
  • a reference numeral 56 represents a pressure sensor for detecting a pressure Pt of the pilot valve 6 in accordance with the manipulation amount of the travelling pedal 6a
  • a reference numeral 95 represents a pressure switch which is switched on when a working pilot pressure Pd is above a predetermined value. The detection result of each sensor and the on/off state of the pressure switch 95 are input to the controller 50.
  • a reference numeral 57 represents a rotational speed setting device for instructing a target rotational speed X in accordance with the manual operation of the fuel lever 57a, and the instructing signal thereof is also input to the controller 50.
  • the controller 50 has a first control circuit unit 60 as shown in Fig. 1 which comprises a load sensing control portion 61 (hereinafter referred to as "LS control portion") for calculating and outputting a first target displacement ⁇ L, a torque control portion 62 for calculating and outputting a second target displacement ⁇ A, a stand-by flow rate control portion 63 for outputting a third target displacement ⁇ O in place of the first target displacement ⁇ L to increase the stand-by flow rate, a minimum-value selecting portion 64 for selecting smaller one of the first or third target displacement input through the minimum-value selecting portion 64 and the second target displacement input through the torque control portion 62, and a servo control portion 65 for controlling the electromagnetic valves 42 and 43 for displacement-controlling on the basis of the target displacement input from the minimum-value selecting portion 64 and the actual displacement.
  • LS control portion load sensing control portion 61
  • torque control portion 62 for calculating and outputting a second target displacement ⁇ A
  • a stand-by flow rate control portion 63 for
  • the LS control portion 61 comprises a target difference pressure generator 61a for outputting a signal corresponding to a target difference pressure ⁇ PLSR, a deviator for calculating a deviation ⁇ (PLS) between the target difference pressure ⁇ PLSR and the difference pressure ⁇ PLS detected by the difference pressure sensor 54, a calculator 61c for calculating a variation ⁇ L of the target value based on the deviation ⁇ (PLS), and a integrator 61d for integrating ⁇ L to calculate the first target displacement ⁇ L for the load sensing control and outputting the calculated value.
  • PLS control portion 61 comprises a target difference pressure generator 61a for outputting a signal corresponding to a target difference pressure ⁇ PLSR, a deviator for calculating a deviation ⁇ (PLS) between the target difference pressure ⁇ PLSR and the difference pressure ⁇ PLS detected by the difference pressure sensor 54, a calculator 61c for calculating a variation ⁇ L of the target value based on the deviation ⁇ (PLS), and
  • the torque control portion 62 comprises a deviator 62a for calculating a surplus torque ⁇ T on the basis of a deviation between the engine rotational speed Nr which is detected by the rotational speed sensor 53 and the control rotational speed N ⁇ represented by the displacement amount of the governor lever which is detected by the potentiometer 55, a target torque calculator 62b for calculating a target torque Tpo for preventing the engine stall on the basis of the surplus torque ⁇ T, a reciprocal calculator 62c for calculating a reciprocal of the pump delivery pressure Pp detected by the pressure sensor 52, a ⁇ ps calculator 62d for calculating a tilt angle ⁇ ps by multiplying the target torque Tpo by the reciprocal 1/Pp, and a filter 62e for subjecting the tilt angle ⁇ ps to a filtering serving as a temporarily-delayed element to output a second target displacement ⁇ A for the input torque limiting control.
  • the stand-by flow rate control portion 63 comprises a stand-by flow rate setting unit 63a for outputting a value corresponding to a third target displacement ⁇ O which is at least larger than the minimum value of the first target displacement ⁇ L calculated in the LS control portion 61, a switch 63b which is closed to output the third target displacement ⁇ O when the response speed selecting switch SW3 is switched on, and a maximum-value selecting portion 63c for selecting and outputting larger one of the first target displacement ⁇ L and the third target displacement ⁇ O.
  • the maximum-value selecting portion 63c inputs larger one of the first target displacement ⁇ L and the third target displacement ⁇ O to the minimum-value selecting portion 64.
  • the minimum-value selecting portion 64 selects smaller one of the first or third target displacement ⁇ L or ⁇ O and the second target displacement ⁇ A to input the selected value to the servo control portion 65 as a tilt angle instructing value ⁇ r.
  • the servo control portion 65 includes a deviator 65a for calculating a deviation between the selected tilt angle instructing value ⁇ r and a tilt angle feedback value ⁇ s detected by the tilt angle sensor 51, and a function generator 65b for outputting an on-signal to the electromagnetic value 42 or 43 when ⁇ s is larger than a value of insensitivity range, and controls the tilt angle control device 40 so that the pump tilt angle ⁇ s is coincident with the tile angle instructing value ⁇ r.
  • the second target displacement calculated in the input torque control portion 62 becomes the maximum-value ⁇ Amax as described above. Therefore, the minimum-value selecting portion 64 selects the third target displacement ⁇ O which is set in the stand-by flow rate control portion 63, and the stand-by flow rate of the hydraulic pump 1 becomes a relatively large delivery flow rate Qq (> Qs) which is represented by the product of the third target displacement ⁇ O and the engine rotational speed.
  • the load sensing control calculation as described above is carried out in the LS control portion 61, and the opening of the control valve 20A is increased in proportion to the manipulating amount of the manipulating lever 58 to increase the required delivery flow rate.
  • the first target displacement ⁇ L is increased.
  • the displacement of the hydraulic pump 1 is set to the third target displacement value ⁇ O until the first target displacement ⁇ L is larger than the third target displacement ⁇ O. Therefore, if the quick mode is selected in an operating condition in which the manipulating lever 58 is rapidly manipulated, the pump delivery flow rate is increased with high responsibility while following the manipulation of the manipulating lever 58 because the stand-by flow rate is relatively large.
  • the minimum-value selecting portion 64 when the second target displacement ⁇ A is larger than the third target displacement ⁇ O or first target displacement ⁇ L, the minimum-value selecting portion 64 also selects the second target displacement ⁇ A, and thus the input torque of the pump is prevent from exceeding the output torque of the engine.
  • the displacement of the hydraulic pump 1, that is, the stand-by flow rate can be altered by the manipulation of the response speed selecting switch SW3, so that the actuator is moderately operated in accordance with the fine manipulation of the operating member to thereby improve the fine operation in the normal mode where the stand-by flow rate is small while the actuator is quickly operated in accordance with the rapid manipulation of the operating member to thereby improve the responsibility in the quick mode where the stand-by flow rate is large.
  • Fig. 1 if the third target displacement ⁇ O is set to be larger than the maximum value ⁇ Amax output from the input torque control portion 62, the displacement of the pump is controlled through the input torque control at all times when the response speed selecting switch SW3 is switched on while the displacement of the pump is controlled through any one of the load sensing control and the input torque control in accordance with the operating condition when the switch SW3 is switched off.
  • the response speed selecting switch SW3 may comprise a pressure switch which is switched on, for example, when the travelling pilot pressure is above a predetermined value. With this construction, at the vehicle travelling, the stand-by flow rate becomes larger and thus the responsibility of the start of the vehicle travelling can be improved. Further, a pressure switch, which is switched on by the pilot pressure for controlling actuators for which another responsibility is required other than the actuator of the vehicle travelling, may be provided in place of the response speed selecting switch SW3, and both of this pressure switch and the response speed selecting switch SW3 may be provided.
  • Fig. 4 shows a second embodiment.
  • the third target displacement ⁇ O for altering the stand-by flow rate is a fixed value.
  • the third target displacement ⁇ O can be set to any value in accordance with a manipulation amount of an operation member by the operator.
  • a response selection dial DI such as a volume for outputting an electrical signal in accordance with a rotation manipulating amount thereof is provided in place of the response speed selecting switch SW3, and the stand-by flow rate control portion 63A is provided with a function generator 63d for outputting a third target displacement ⁇ O in accordance with the output voltage of the dial DI in place of the setting unit 63a and the switch 63b.
  • the stand-by flow rate can be set to any value in accordance with an operator's preference or an operating condition, and thus a hydraulic construction machine which is favorite for any one and has such an improved operation performance as to be broadly matched with various operating conditions can be provided.
  • the displacement of the pump can be controlled only through the input torque control in the same manner as described above.
  • Figs. 5 to 7 show a third embodiment.
  • the stand-by flow rate control portions 63 and 63A are provided independently of each of the LS control portion 61 outputting the first target displacement ⁇ L and the input control portion 62 outputting the second target displacement ⁇ O, and the stand-by flow rate is altered through the manipulation of the operation member by the operator.
  • the stand-by delivery flow rate control portion is omitted, and the load sensing control is inhibited when a special operating condition is detected to thereby control the displacement of the hydraulic pump through the input torque limiting control.
  • the load sensing control and the input torque limiting control are selectively carried out, and when the work is carried out using the manipulating lever 58 together with controlling the engine rotational speed by the travelling pedal 6a, the input torque limiting control is carried out using no load sensing control.
  • the controller 50 is equipped with a first control circuit portion 60B as shown in Fig. 5 and a second control circuit portion 80 as shown in Fig. 6.
  • the first control circuit portion 60B as shown in Fig. 5 the stand-by flow rate control portion 63 as shown in Fig. 1 is omitted, a selection switch 66 is provided at a rear stage of the minimum-value selecting portion 64, and a judgement portion 67 serving as a switch control portion of the switch 66 is provided.
  • the judgment portion 67 includes a comparator 67a and an AND gate circuit 67a, and it is so constructed that it outputs a high-level signal when the manipulating lever 58 is manipulated while the engine rotational speed is controlled by the travelling pedal 6a, so that the work is carried out.
  • the comparator 67a outputs a high-level signal when the pilot pressure Pt detected by the pressure sensor 56 is higher than a predetermined pressure which is beforehand set (by a reference power supply 67c), and the output signal thereof is input to the AND gate circuit 67b.
  • the AND gate circuit 67b is also supplied with a signal representing an on/off state of the brake switch SW2 and a signal representing a switching state of the forward/reverse travel change-over switch SW1, and the AND gate circuit 67b is enabled when the following four conditions are wholly satisfied:
  • the selection switch 66 is switched to an a-contact point when the AND gate circuit 67b is in off-state (when the low-level signal is output and the vehicle travels) to select the output of the minimum-value selecting portion 64. That is, smaller one of the first target displacement ⁇ L and the second target displacement ⁇ A is selected as the displacement instructing value ⁇ r.
  • the selection switch 66 is switched to a b-contact point to select the output of the torque control portion 62. That is, the second target displacement ⁇ A is selected as the displacement target instructing value ⁇ r.
  • the selected displacement instructing value ⁇ r is input to the servo control portion 66.
  • the controller 50 also includes the second control circuit portion 80 as shown in Fig. 6.
  • a reference numeral 81 represents a first target rotational speed calculating portion to which a signal corresponding to the manipulation amount X of the fuel lever 57a of the rotational speed setting device 57 is input to determine a first target rotational speed Nx which corresponds to the manipulation amount X.
  • a reference numeral 82 represents a second target rotational speed calculating portion supplied with the pilot pressure Pt detected by the pressure sensor 56 which indicates the manipulation amount of the travelling pedal 6a, and it serves to determine a second target rotational speed Nt which corresponds to the pilot pressure Pt.
  • the manipulation amount X and the first target rotational speed Nx are set in such a relationship that the first target rotational speed Nx is linearly increased from an idle rotational speed Ni as the displacement amount X is increased.
  • the pilot pressure Pt and the second target rotational speed Nt are set in such a relationship that the second target rotational speed Nt is linearly increased from the idle rotational speed Ni as the pilot pressure Pt (pedal manipulation amount) is increased.
  • the maximum value Nxmax of the first target rotational speed Nx is set to be lower than the maximum rotational speed which can be output by the engine 27, and the maximum value Ntmax of the second target rotational speed Nt is set to be substantially equal to the maximum rotational speed of the engine 27. Therefore, the maximum value Ntmax of the target rotational speed Nt is larger than the maximum value Nxmax of the target rotational speed Nx.
  • the target rotational speed instructing value Ny is compared with the control rotational speed N ⁇ indicated with the displacement amount of the governor lever 27b which is detected by the potentiometer 55, and the pulse motor 28 is so controlled that both are coincident with each other in accordance with the procedure as shown in Fig. 7.
  • step S21 in Fig. 7 the target rotational speed instructing value Ny and the control rotational speed N ⁇ indicated with the displacement amount of the governor lever are read in, and the process goes to a step S22.
  • a result of N ⁇ - Ny is stored as a difference rotational speed A in a memory, and at a step S23 it is judged on the basis of a predetermined reference difference rotational speed K as to whether
  • the control rotational speed N ⁇ indicated by the displacement amount of the governor lever is larger than the target rotational speed instructing value Ny, that is, the control rotational speed is larger than the target rotational speed. Therefore at a step S25, a signal instructing the reverse rotation of the motor is output to the pulse motor 28 to decrease the engine rotational speed. Through this operation, the pulse motor 28 is reversely rotated and the rotational speed of the engine 27 is reduced.
  • the brake switch SW2 When the work such as a digging is carried out by driving the front attachment, the brake switch SW2 is switched on and the forward/reverse travelling change-over switch SW1 is switched to the N-position.
  • the control of the engine rotational speed can be performed by the fuel lever 57a or the travelling pedal 6a.
  • the fuel lever 57a of the rotational speed setting device 57 is kept at the maximum stroke position or at a proper intermediate position of a stroke lower than the maximum stroke.
  • the travelling pilot pressure Pt which is input to the second target rotational speed calculating portion 82 of the second control circuit portion 80 is zero, so that the second target rotational speed Nt calculated in the above calculating portion 82 becomes the idle rotational speed Ni.
  • the manipulation amount X of the fuel lever which is input to the first target rotational speed calculating portion 81 is a larger value other than zero, so that the first target rotational speed Nx calculated in the above calculating portion 81 becomes a value which is lager than the idle rotational speed Ni and corresponds to the stroke position of the fuel lever 57a.
  • the target rotational speed Nx is selected as the target rotational speed instructing value Ny, and the engine 27 is controlled to the target rotational speed Nx.
  • the engine rotational speed is controlled so as to be kept to a constant speed which corresponds to the stroke position of the fuel lever.
  • the brake switch SW2 is switched on and the forward/reverse travelling change-over switch SW1 is in its N-position (neutral position), and the pressure switch 95 is switched on through the manipulation of the working lever 58.
  • the pilot pressure Pt is lower than the predetermined value because the travelling pedal 6a is not manipulated (the conditions (1), (2) and (4) of the conditions (1), (2), (3) and (4) as described above are satisfied, but the condition (3) is not satisfied), and the AND gate circuit 67b constituting the judging portion 67 is enabled. Therefore, the selecting switch 66 selects the signal from the minimum-value selecting portion 64. That is, smaller one of the first and third target displacements ⁇ L and ⁇ A is selected as the displacement instructing value ⁇ r, and the displacement of the hydraulic pump 1 is controlled so as to be equal to the selected displacement instructing value ⁇ r.
  • the delivery pressure of the hydraulic pump 1 is controlled so as to be higher than the load pressure of the hydraulic motor 3 by the target difference pressure ⁇ PLSR using the first target displacement ⁇ L (the load sensing control is carried out), and the input torque of the hydraulic pump 1 is controlled so as not to exceed the target torque Tp0 using the second target displacement ⁇ A (the input torque limiting control is carried out).
  • the selecting switch 66 is switched to the a-contact because the brake switch SW2 is switched off, and the pump tilt angle is controlled with smaller one of ⁇ L and ⁇ A.
  • the brake switch SW is switched on, the forward/reverse switch SW1 is switched to the neutral N-position, and the fuel lever 57a is kept at the minimum stroke position.
  • the second target rotational speed calculating portion 82 is supplied with the travelling pilot pressure Pt corresponding to the manipulation amount (step-on amount) of the travelling pedal 6a, so that the second target rotational speed Nt calculated in the calculating portion 82 becomes a value which is higher than the idle rotational speed Ni and corresponds to the manipulation amount of the travelling pedal 6a. Therefore, the target rotational speed Nt is selected as the target rotational speed instructing value Ny in the selecting portion 83, and the rotational speed of the engine 27 is controlled to the target rotational speed Nt.
  • the engine rotational speed is controlled in accordance with the operation amount of the travelling pedal 6a, so that the engine rotational speed is increased as the operation amount of the travelling pedal 6a is increased while the engine rotational speed is decreased as the travelling pedal 6a is returned.
  • the brake switch SW2 is turned on, the forward/reverse change-over switch SW1 is in its N-position (neutral position), the pilot pressure Pt has a value higher than the predetermined value through the operation of the travelling pedal 6a, and the pressure switch 95 is switched on by manipulating the working lever 58. Therefore, all of the conditions (1), (2), (3) and (4) as described above are satisfied, so that the AND gate circuit 67b serving as the judging portion 67 is enabled. Through this operation, the selecting switch 66 is switched to the b-contact point, so that the second target displacement ⁇ A calculated in the torque control portion 62 is selected as the displacement instructing value ⁇ r.
  • the displacement of the hydraulic pump 1 is so controlled as to be equal to the selected displacement instructing value ⁇ r. That is, the load sensing control as described above is not carried out, and only the input torque limiting control is carried out. Therefore, in a range below the second target displacement which is determined by the input torque control, the delivery flow rate of the hydraulic pump 1 is increased or decreased substantially in proportion to the above-described increase/decrease control of the engine rotational speed using the travelling pedal 6a, so that the driving of the front attachment such as the boom can be controlled at a desired speed.
  • the selecting switch 66 as shown in Fig. 5 is so designed as to be freely switchable by the operator, the selective use of the load sensing control and the input torque control can be performed on the basis of the operator's judgment.
  • the same effect as the third embodiment can be obtained.
  • the existing travelling pedal 6a is also used as operating means for the engine rotational speed control.
  • the operating means is not limited to the travelling pedal 6a, and may be another operation member (preferably, a pedal).
  • the travelling hydraulic motor 4 and the working hydraulic cylinder 20A are provided as the hydraulic actuator.
  • the hydraulic actuator may be constructed so as to have plural working hydraulic cylinders 20A and a hydraulic motor for a turning of the upper swing body of the vehicle.
  • the working hydraulic cylinder 20A is not limited to a cylinder for driving of the boom, and may be a cylinder for driving of the arm or the bucket.
  • a function that the stand-by flow rate is controlled is added to this third embodiment by adding the response speed selecting switch SW3 and the stand-by flow rate control portion 63 of the first embodiment.
  • Fig. 12 shows a block diagram of this variation.
  • Fig. 8 is a detailed block diagram of the torque control portion 62 of the first to third embodiments as described above.
  • the control rotational speed N ⁇ which corresponds to the governor lever position detected by the potentiometer 55 is input to a reference rotational speed calculating portion 162a and a torque calculating portion 162b.
  • the reference rotational speed calculating portion 162a calculates a speed sensing reference rotational speed Ns in accordance with the input control rotational speed N ⁇ on the basis of a characteristic as shown in the figure.
  • the reference rotational speed Ns is increased as the control rotational speed N ⁇ is increased.
  • the torque calculating portion 162b calculates the target torque Tro in accordance with the input control rotational speed N ⁇ on the basis of a characteristic as shown in the figure.
  • the correction torque is positive when the rotational speed deviation ⁇ N is positive, and is negative when the rotational speed deviation ⁇ N is negative.
  • is increased with increase of
  • a function generator 162e outputs a signal representing "0" when the control rotational speed N ⁇ is lower than a predetermined value, and "1" when the control rotational speed N ⁇ is equal to or above the predetermined value, and the signal is multiplied by the correction torque ⁇ T in a multiplier 162f. That is, the correction torque ⁇ T is effective only when the control rotational speed N ⁇ is equal to or above the predetermined value.
  • ⁇ T is added to the target torque Tro as described above in the adder 162g, and the result of this addition is output as the target torque instructing value Tpo.
  • the target displacement ⁇ A is calculated on the basis of the target torque instructing value Tpo.
  • the correction torque ⁇ T becomes positive so as to cause the target torque instructing value Tpo to be increased.
  • the correction torque ⁇ T becomes negative so as to cause the target torque instructing value Tpo to be decreased. Therefore, the target torque can be approached to a rated torque, and thus the torque can be effectively set.
  • the governor lever 27 When the travelling pedal 6a is rapidly stepped on to a full throttle position, the governor lever 27 is immediately operated to a full throttle position by the pulse motor 28, so that the control rotational speed N ⁇ is increased, and the speed sensing reference rotational speed Ns is also immediately increased.
  • the operation amount of the governor lever reaches the maximum value, there is a time lag until the actual rotational speed of the engine is increased up to its maximum value.
  • the rotational speed deviation ⁇ N is negative during this time lag, and the correction torque ⁇ T is also negative. Therefore, the target torque instructing value Tpo is lowered, so that the displacement of the hydraulic pump is decreased, and the rise-up of the rotational speed is deteriorated.
  • Fig. 9 shows the input torque control portion 162 of the first control circuit portion 60 inside of the controller 50.
  • the same elements as those of Fig. 8 are represented by the same reference numerals, and the difference point will be mainly described.
  • the input torque control portion 162 is equipped with a torque calculating portion 162k in parallel to the torque calculating portion 162d.
  • the torque calculation portion 162k has a different characteristic from those of the torque calculation portion 162d.
  • the output value of each torque calculating portion is input to the selecting portion 162h.
  • the correction torque ⁇ T becomes positive and increases with increase of ⁇ N when the rotational speed deviation ⁇ N is positive.
  • ⁇ N is negative
  • ⁇ T is zero. That is, only a control for increase of input torque is carried out.
  • the input torque control portion 162 includes an AND gate circuit 162i, and the AND gate circuit 162i is input with a signal representing an on/off state of the brake switch SW2, a signal representing a manipulation position of the forward/reverse change-over switch SW1, and an output of a function generator 162j.
  • the function generator 162j outputs "1" when an operation amount of the travelling pedal 6a is equal to or above a predetermined amount, and "0" when it is smaller than the predetermined amount, and is supplied with a signal Pt representing the operation amount of the travelling pedal 6a which is an output of the pressure sensor 56. Therefore, when the following conditions are satisfied, that is, when the vehicle travels the AND gate circuit 162i is enabled to input a high-level signal to a selection switch 162h, and the selection switch 162h selects the torque calculating portion 162k:
  • the control rotational speed N ⁇ which is a detection value of the governor lever position becomes the maximum value, and interlockingly with the maximum value of the control rotational speed, the speed sensing reference rotational speed Ns also becomes the maximum value.
  • a time lag is required until the actual rotational speed of the engine reaches a value corresponding to the maximum value of the governor lever, and during this time lag the rotational speed deviation ⁇ N is negative.
  • the correction torque ⁇ T is not negative and is equal to zero even when the rotational speed deviation ⁇ N becomes negative. Therefore, the target torque instructing value Tpo is not reduced, and the displacement of the hydraulic pump 1 is not reduced, so that the acceleration performance for vehicle travelling in this case can be more improved than that in the case of using the input torque control portion as shown in Fig. 8.
  • the torque calculating portion 162d is selected by the selection switch 162h in a non-travelling operation such as a digging work, like the conventional input torque control portion, the pump displacement is reduced to reduce the engine input torque when the engine has no surplus for the torque, so that the useless engine stall can be prevented.
  • Such a construction for assuring the acceleration performance may be applied to a turning operation of the upper swing body of the vehicle as well as a travelling operation.
  • the hydraulic control apparatus of this invention as described above is effectively applied particularly to various hydraulic construction machines equipped with a diesel engine, such as a wheel-type hydraulic shovel, a crawler-type hydraulic shovel, a hydraulic crawler crane, a wheel loader, etc.

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mining & Mineral Resources (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • Operation Control Of Excavators (AREA)
  • Fluid-Pressure Circuits (AREA)
  • Control Of Positive-Displacement Pumps (AREA)
EP96203352A 1991-01-28 1992-01-28 Dispositif de commande hydraulique pour engin de chantier Expired - Lifetime EP0765970B1 (fr)

Applications Claiming Priority (7)

Application Number Priority Date Filing Date Title
JP2691291 1991-01-28
JP26912/91 1991-01-28
JP2691291 1991-01-28
JP18480291 1991-07-24
JP184802/91 1991-07-24
JP18480291 1991-07-24
EP92903709A EP0522171B1 (fr) 1991-01-28 1992-01-28 Systeme de commande hydraulique pour engins de chantier hydrauliques

Related Parent Applications (2)

Application Number Title Priority Date Filing Date
EP92903709A Division EP0522171B1 (fr) 1991-01-28 1992-01-28 Systeme de commande hydraulique pour engins de chantier hydrauliques
EP92903709.1 Division 1992-08-08

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EP0765970A2 true EP0765970A2 (fr) 1997-04-02
EP0765970A3 EP0765970A3 (fr) 1997-07-23
EP0765970B1 EP0765970B1 (fr) 2001-04-04

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EP96203352A Expired - Lifetime EP0765970B1 (fr) 1991-01-28 1992-01-28 Dispositif de commande hydraulique pour engin de chantier
EP92903709A Expired - Lifetime EP0522171B1 (fr) 1991-01-28 1992-01-28 Systeme de commande hydraulique pour engins de chantier hydrauliques

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US (1) US5307631A (fr)
EP (2) EP0765970B1 (fr)
KR (1) KR970000491B1 (fr)
DE (2) DE69231776T2 (fr)
WO (1) WO1992013144A1 (fr)

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US4672811A (en) * 1984-04-17 1987-06-16 Kabushiki Kaisha Komatsu Seisakubsho Vehicle speed control system
US4704866A (en) * 1984-06-04 1987-11-10 Sundstrand Corporation Automatic travel speed control for a harvesting machine
EP0326150A1 (fr) * 1988-01-27 1989-08-02 Hitachi Construction Machinery Co., Ltd. Système de commande sensible à la charge pour un circuit hydraulique
EP0353799A1 (fr) * 1988-07-04 1990-02-07 Hitachi Construction Machinery Co., Ltd. Dispositif pour régler la vitesse de rotation d'un engin de terrassement
EP0379595A1 (fr) * 1988-07-08 1990-08-01 Hitachi Construction Machinery Co., Ltd. Appareil hydrodynamique
EP0432266A1 (fr) * 1989-01-18 1991-06-19 Hitachi Construction Machinery Co., Ltd. Unite de commande hydraulique pour engin de construction

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0906993A2 (fr) * 1997-10-02 1999-04-07 Hitachi Construction Machinery Co., Ltd. Système d'accélération automatique pour une machine motrice d'un engin de terrassement et système de commande de la machine motrice et de la pompe hydraulique
EP0906993A3 (fr) * 1997-10-02 1999-10-20 Hitachi Construction Machinery Co., Ltd. Système d'accélération automatique pour une machine motrice d'un engin de terrassement et système de commande de la machine motrice et de la pompe hydraulique
EP0908564A2 (fr) * 1997-10-08 1999-04-14 Hitachi Construction Machinery Co., Ltd. Système de commande pour la machine motrice et la pompe hydraulique d'un engin de terrassement
EP0908564A3 (fr) * 1997-10-08 1999-11-17 Hitachi Construction Machinery Co., Ltd. Système de commande pour la machine motrice et la pompe hydraulique d'un engin de terrassement
WO1999054557A1 (fr) * 1998-04-23 1999-10-28 Caterpillar Inc. Appareil et procede de reglage d'une pompe a cylindree variable
US6073442A (en) * 1998-04-23 2000-06-13 Caterpillar Inc. Apparatus and method for controlling a variable displacement pump
FR2799776A1 (fr) * 1999-10-19 2001-04-20 Sumitomo Constr Machinery Mfg Unite de commande pour engin de chantier
EP1550809A1 (fr) * 2002-09-26 2005-07-06 Hitachi Construction Machinery Co., Ltd. Controleur pour engin de travaux et procede de fonctionnement du couple d'entree
WO2004029460A1 (fr) 2002-09-26 2004-04-08 Hitachi Construction Machinery Co., Ltd. Controleur pour engin de travaux et procede de fonctionnement du couple d'entree
EP1550803A1 (fr) * 2002-09-26 2005-07-06 Hitachi Construction Machinery Co., Ltd Controleur de force motrice d'amor age d'un engin de travaux
EP1550803A4 (fr) * 2002-09-26 2007-04-25 Hitachi Construction Machinery Controleur de force motrice d'amor age d'un engin de travaux
US7886862B2 (en) 2002-09-26 2011-02-15 Hitachi Construction Machinery Co., Ltd. Prime mover control device of construction machine
EP1550809A4 (fr) * 2002-09-26 2011-04-27 Hitachi Construction Machinery Controleur pour engin de travaux et procede de fonctionnement du couple d'entree
WO2008135303A1 (fr) * 2007-05-02 2008-11-13 Robert Bosch Gmbh Agencement de soupape avec un manomètre à piston individuel et une soupape de frein d'abaissement
US8516944B2 (en) 2007-05-02 2013-08-27 Robert Bosch Gmbh Valve arrangement having individual pressure scale and load-lowering valve
CN107420378A (zh) * 2017-06-28 2017-12-01 合肥工业大学 一种液压机驱动系统匹配节能方式

Also Published As

Publication number Publication date
US5307631A (en) 1994-05-03
DE69220293T2 (de) 1998-01-22
DE69220293D1 (de) 1997-07-17
WO1992013144A1 (fr) 1992-08-06
EP0765970A3 (fr) 1997-07-23
EP0522171B1 (fr) 1997-06-11
EP0522171A4 (en) 1993-09-08
DE69231776T2 (de) 2001-09-13
EP0765970B1 (fr) 2001-04-04
KR930700738A (ko) 1993-03-16
DE69231776D1 (de) 2001-05-10
KR970000491B1 (ko) 1997-01-13
EP0522171A1 (fr) 1993-01-13

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